Reasoning is not right for Tharkun, but I think I may have had a hand in that.
Stone-folk was meant to refer to the people of Gondor, which translates as Stone-land. They are called Tarks by orcs. Tharkun is tark overlapping with hun.
As for #4, many right elements but wrong person. I can only think of two other Ringbearers off the top of my head whose names start with G.
1.
SAURON Finnish invention replaced article with conjunction, tangled lord.
2.
ESIWMAS Hobbit's reflection confuses action and location of fish.
3.
ANNATAR Rodent jumped back after girl beguiled Elves.
4.
G____ Small big boy girl puzzled king.
5.
BILBO I replaced you in plant part before exclamation was heard by hobbit.
6.
DEAGOL Leave in the middle of a bargain? Don't want to share assets.
7.
ALATARIEL Science fiction princess lies back on top of sacrificial table for a crowned maiden.
8.
THARKUN One of stone folk stumbles over nomad wizard.
9.
NERWEN Revive muddled point, get near-palindrome.
10.
CELEBRIMBOR Dazed, cropped element joins thankless star for smith.